19 research outputs found
Electron-Phonon Interactions and the Intrinsic Electrical Resistivity of Graphene
We present a first-principles study of the temperature- and density-dependent
intrinsic electrical resistivity of graphene. We use density-functional theory
and density-functional perturbation theory together with very accurate Wannier
interpolations to compute all electronic and vibrational properties and
electron-phonon coupling matrix elements; the phonon-limited resistivity is
then calculated within a Boltzmann-transport approach. An effective
tight-binding model, validated against first-principles results, is also used
to study the role of electron-electron interactions at the level of many-body
perturbation theory. The results found are in excellent agreement with recent
experimental data on graphene samples at high carrier densities and elucidate
the role of the different phonon modes in limiting electron mobility. Moreover,
we find that the resistivity arising from scattering with transverse acoustic
phonons is 2.5 times higher than that from longitudinal acoustic phonons. Last,
high-energy, optical, and zone-boundary phonons contribute as much as acoustic
phonons to the intrinsic electrical resistivity even at room temperature and
become dominant at higher temperatures.Comment: 7 pages 5 figure
Fermi-Energy-Dependent Structural Deformation of Chiral Single-Wall Carbon Nanotubes
In this work, we use an extended tight-binding approach for calculating the Fermi-energy dependence of the structural deformation of chiral single-wall carbon nanotubes (SWNTs). We show that, in general, nanotube strains occur in such a way as to avoid a net charge from being accumulated on the nanotube. We also investigate the effect of the Fermi-energy-induced strains on the electronic structure of SWNTs, showing that the optical transition energies change by up to 0.5 eV due to the induced strains and that this change is nearly independent of how the nanotube is deformed. Finally, we also consider the contribution of the electron-electron Coulomb repulsion to the total energy by using an effective regularized potential energy model. We show that the inclusion of the Coulomb repulsion leads to larger strains and smaller net charges transferred to the nanotube.National Science Foundation (U.S.) (Grant DMR-1004147
Coulomb-hole summations and energies for GW calculations with limited number of empty orbitals: a modified static remainder approach
Ab initio GW calculations are a standard method for computing the
spectroscopic properties of many materials. The most computationally expensive
part in conventional implementations of the method is the generation and
summation over the large number of empty orbitals required to converge the
electron self energy. We propose a scheme to reduce the summation over empty
states by the use of a modified static-remainder approximation, which is simple
to implement and yields accurate self energies for both bulk and molecular
systems requiring a small fraction of the typical number of empty orbitals
Role of solvent-anion charge transfer in oxidative degradation of battery electrolytes
Electrochemical stability windows of electrolytes largely determine the limitations of operating regimes of lithium-ion batteries, but the degradation mechanisms are difficult to characterize and poorly understood. Using computational quantum chemistry to investigate the oxidative decomposition that govern voltage stability of multi-component organic electrolytes, we find that electrolyte decomposition is a process involving the solvent and the salt anion and requires explicit treatment of their coupling. We find that the ionization potential of the solvent-anion system is often lower than that of the isolated solvent or the anion. This mutual weakening effect is explained by the formation of the anion-solvent charge-transfer complex, which we study for 16 anion-solvent combinations. This understanding of the oxidation mechanism allows the formulation of a simple predictive model that explains experimentally observed trends in the onset voltages of degradation of electrolytes near the cathode. This model opens opportunities for rapid rational design of stable electrolytes for high-energy batteries
BerkeleyGW: A Massively Parallel Computer Package for the Calculation of the Quasiparticle and Optical Properties of Materials and Nanostructures
BerkeleyGW is a massively parallel computational package for electron
excited-state properties that is based on the many-body perturbation theory
employing the ab initio GW and GW plus Bethe-Salpeter equation methodology. It
can be used in conjunction with many density-functional theory codes for
ground-state properties, including PARATEC, PARSEC, Quantum ESPRESSO, OCTOPUS
and SIESTA. The package can be used to compute the electronic and optical
properties of a wide variety of material systems from bulk semiconductors and
metals to nanostructured materials and molecules. The package scales to
10,000's of CPUs and can be used to study systems containing up to 100's of
atoms
Quantum-centric Supercomputing for Materials Science: A Perspective on Challenges and Future Directions
Computational models are an essential tool for the design, characterization,
and discovery of novel materials. Hard computational tasks in materials science
stretch the limits of existing high-performance supercomputing centers,
consuming much of their simulation, analysis, and data resources. Quantum
computing, on the other hand, is an emerging technology with the potential to
accelerate many of the computational tasks needed for materials science. In
order to do that, the quantum technology must interact with conventional
high-performance computing in several ways: approximate results validation,
identification of hard problems, and synergies in quantum-centric
supercomputing. In this paper, we provide a perspective on how quantum-centric
supercomputing can help address critical computational problems in materials
science, the challenges to face in order to solve representative use cases, and
new suggested directions.Comment: 60 pages, 14 figures; comments welcom